RAM air turbine driving a variable displacement hydraulic pump

ABSTRACT

An improved RAM air turbine (30) for the generation of emergency power on an airplane is disclosed. The RAM air turbine has an operational range in which reduced power is produced by a power controller (40) at speeds at which stalling of the RAM air turbine would occur under the control of a governor (16) which adjusts the pitch of the blades (12) of the turbine in combination with a pressure regulator (150) controlling the output of pressurized hydraulic fluid from a variable displacement hydraulic pump (19).

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to patent application Ser. No. 539,200, entitled "RAMAir Turbine With Power Controller and Method of Operation", filed oneven date herewith, which is assigned to the Assignee of the presentinvention, which application is incorporated by reference in itsentirety; and to patent application Ser. No. 539,749, entitled "RAM AirTurbine With Power Controller With Disabling Mechanism of PowerController and Method of Operation", filed on even date herewith, whichis assigned to the Assignee of the present application, whichapplication is incorporated herein by reference in its entirety; and topatent application Ser. No. 539,598 entitled "RAM Air Turbine WithOperation in Plural Speed Ranges", filed on even date herewith, which isassigned to the Assignee of the present invention, which application isincorporated herein by reference in its entirety.

DESCRIPTION

1. Technical Field

The present invention relates to RAM air turbines used by airplanes forgenerating emergency power.

2. Background Art

Hydraulic and electric power is generated in airplanes by power takeoffsfrom the propulsion engines during flight and/or an auxiliary powerunit. Control of an airplane is dependent upon the generation ofelectrical and/or hydraulic power. In the event that the propulsionengines are rendered inoperative during flight and emergency powercannot be generated by the APU, control of the airplane may not bemaintained without an emergency power source which generates its powerfrom the movement of the airplane through the air.

FIG. 1 illustrates two types of RAM air turbines which are used togenerate emergency power in modern jet aircraft. A RAM air turbine isstored within (fuselage or wings) the airplane except during deploymentfor purposes of generating emergency power. Upon deployment, the RAM airturbine pivots from a stowed position within the airplane to a deployedposition which depends downward from the fuselage to a position whereair intercepts the RAM air turbine as a consequence of the velocity ofthe airplane moving through the air. The RAM air turbine 10 has aplurality of blades 12 which are mounted on a hub, not illustrated,which drives an output shaft 14. The RAM air turbine 10 has a governor16 which adjusts the pitch of the blades 12 to maintain operation withina first rotational velocity range which typically varies between 4,000and 6000 rpm. In commercial aircraft prior to the Airbus A330, the shaft14 drove a variable displacement hydraulic pump 18 which produced highpressure hydraulic fluid 20 which was applied to a hydraulic load 32such as a hydraulic motor and/or actuators. When applied to a hydraulicmotor, the hydraulic motor is typically used to drive an electricalpower generator for producing emergency electrical power. When appliedto hydraulic actuators, hydraulically controlled elements, such as wingflaps are activated.

The variable displacement hydraulic pump contains a pressure regulatorwhich regulates the output pressure of the hydraulic fluid 20 in anoperational pressure range such as 3,000 psi±200 psi. The pressureregulator is used to develop a hydraulic displacement control signalwhich varies the displacement of the variable displacement hydraulicpump 18 to control the delivery of pressurized hydraulic fluid to thehydraulic load 32 to be within the pressure range established by thepressure regulator.

The flow rate of hydraulic fluid is controlled by variation ofdisplacement of the variable displacement hydraulic pump 18 such thatthe displacement is inversely proportional to the high pressure outputof the variable displacement motor within the operational pressurerange. The control of the displacement is produced by a stroking pistonwhich varies an angle of inclination of a wobbler to change the lengthof stroke of pistons of the variable displacement hydraulic pump. Thestroking piston applies a force to one side of the wobbler. A ratepiston applies a force to an opposite side of the wobbler. As a result,the displacement of the variable displacement hydraulic pump follows theextension of the stroking piston which varies inversely with the highpressure output of the variable displacement hydraulic pump.

The Airbus A330 contains a gearbox 22 which is driven by the shaftoutput 14. The gearbox 22 drives a variable displacement hydraulic pump18 which functions as described above.

Prior art RAM air turbines are designed to be operated within a speedrange for which the RAM air turbine may produce power without stallingto maintain control of the airplane when other power generating sourcesare not present. This speed range is typically from approximately 450knots, which is the speed of the airframe when flying at normal cruisingspeeds when power from the propulsion engines is lost, to approximately125 knots which is a speed at which a pilot would attempt to land theairplane without operation of the propulsion engines.

The governor 16 usually contains a hydraulically powered pitch controlmechanism which varies the pitch from coarse to fine to provideincreased power generation in response to increased demand for powerfrom the hydraulic load while regulating speed within the firstrotational velocity range as discussed above. Once the pitch of theblades 12 has been adjusted to its finest setting by the pitchadjustment mechanism of the governor 16, increased demand for power bythe hydraulic load leads to stalling with the generated power outputimmediately dropping to zero.

The prior art does not have any mechanism to drop the power output fromthe turbine 10 to prevent stalling other than the aforementioned pitchadjusting mechanism. The ability to generate emergency power at thelower end of the speed range of the aircraft is critical in controllingan airplane during landing procedures when propulsion from thepropulsion engines has been lost. The inability of the pilot to controlcontrol surfaces at speeds at which it is desired to land the airplaneis likely to result in a crash with the attendant loss of life. Theprior art has the deficiency of not extending the lowest velocity atwhich emergency power may be generated below the lowest speed at whichthe pitch adjustment mechanism permits the RAM air turbine to generatepower.

The governor 16 functions to vary the pitch of the blades 12 in a mannerwhich satisfies: the demand for hydraulic power placed upon the variabledisplacement hydraulic pump which outputs pressurized hydraulic fluid atthe regulated pressure within the first rotational velocity range. Thegovernor automatically adjusts the pitch of the blades 12 toward thefinest setting to extract additional power from the RAM airstreamintercepting the blades 12 as the demand for power goes up and/or thevelocity of the aircraft decreases. When the demand for pressurizedhydraulic fluid 20 for driving hydraulic loads exceeds the energyavailable from the RAM airstream when the blades 12 have been adjustedto their finest pitch for providing the maximum energy from the RAMairstream a dangerous stall condition exists at which the RAM airturbine 10 will cease to operate thereby preventing the generation ofany emergency power.

Control of an aircraft could be maintained for velocities of theaircraft at which the pitch control mechanism cannot prevent stalling bythe production of reduced power from the variable displacement hydraulicpump if a mechanism were provided to overcome the stalling of the blades12 as a result of the inability of the governor 16 to prevent stalling.

U.S. Pat. No. 3,125,960 discloses a RAM air turbine for use in anaircraft. The RAM air turbine has a pitch control which varies the pitchof the blades of the RAM air turbine. A fixed displacement hydraulicpump is driven by the rotation of the blades. An unloading valve is usedto unload the hydraulic pump until the blades reach a rotationalvelocity of approximately 1,000 rpm. An accumulator 32 is charged withpressurized hydraulic fluid produced by the turbine driving the fixeddisplacement hydraulic pump. A pressure regulator allows pressurizedhydraulic fluid to be outputted after the accumulator reaches apredetermined pressure of 3,000 lbs. Spool valve 35 controls the portingof pumping pressure to govern the speed of the turbine. The pressurefrom the hydraulic pump is used to control the pitch of the blades toprovide governing action to control the speed of rotation of the blades.

The RAM air turbine disclosed in U.S. Pat. No. 3,125,960 requires thatthe highest pump output be sized below the lowest turbine powerproducing capability for a rated airspeed. If a reduced airflow isencountered, such as that produced by a decreased airspeed in which itis critical to maintain control of flight surfaces, the governor of theRAM air turbine of the '960 patent will adjust the blades to the finestpitch condition in attempting to extract maximum power from theairstream and stall under full pumping load. No mechanism is provided inthe RAM air turbine of the '960 patent to reduce the hydraulic poweroutput to prevent stalling by an overload of power demanded from theturbine. This system functions to produce a regulated pressure output ofhydraulic fluid similar to the operation of the prior art described withrespect to FIG. 1.

RAM air turbines for generating emergency power on an airplane aredisclosed in additional patents. See U.S. Pat. Nos. 3,149,678 and4,717,095 and 4,742,976 assigned to the assignee of the presentinvention. None of these patents addresses the deficiency of the priorart in providing a mechanism for generating emergency power in arotational velocity range of the blades of a RAM air turbine at whichthe pitch adjustment mechanism cannot prevent stalling.

Volumetric fuses are used in the prior art during starting to bypass thehigh pressure output of the variable displacement hydraulic pump drivenby the RAM air turbine to the low pressure input for a predeterminedvolume of hydraulic fluid to unload the blades of the turbine to permitreaching the speed control range of the governor. Volumetric fuses arehydraulically complex, add weight and do not permit a determination ofwhether resetting has occurred. If resetting does not occur, theunloading of the blades will not occur which prevents starting of theRAM air turbine with potentially disastrous consequences.

DISCLOSURE OF INVENTION

The present invention provides an improved RAM air turbine and method ofoperation in which emergency power is produced for airspeeds below whichstalling of the RAM air turbine would occur with the prior art. With theinvention, reduced power is outputted by the RAM air turbine in a secondrotational velocity range lower than the first rotational velocity rangeat which the governor controls the speed of rotation of the blades ofthe RAM air turbine. Emergency power is provided in the secondrotational velocity range by controlling the displacement of a variabledisplacement hydraulic pump such that the level of hydraulic powerproduced by the variable displacement hydraulic pump does not stall theblades of the RAM air turbine. Displacement of the variable displacementhydraulic pump in a first rotational velocity range of the blades iscontrolled in accordance with a conventional stroking piston of theprior art and displacement of the variable displacement hydraulic pumpin the second rotational velocity range is controlled by an anti-stallpiston which is controlled by the output of a speed detector. Theanti-stall piston functions as a variable stop for the stroking pistonin the second rotational velocity range. The speed detector outputcontrols the variable displacement hydraulic pump to produce constantoutput power of a variable flow rate and pressure of hydraulic fluid forany given rotational velocity within the second rotational velocityrange. The constant power output produced by the variable displacementhydraulic pump for blade velocities within the second rotationalvelocity range provides for a reduced power output when compared to thepower which may be outputted by the variable displacement hydraulic pumpin the first rotational velocity range. The reduced power output may beused to control hydraulic loads such as flight control surfaces or ahydraulic motor driving an electrical power generator for generatingemergency power necessary to control the aircraft at speeds below whichheretofore the prior art RAM air turbines would stall.

With the invention, the displacement of the variable displacementhydraulic motor in the first and second rotational velocity ranges iscontrolled by two hydraulic signals. Control in the second rotationalvelocity range of the displacement of the variable displacementhydraulic pump to prevent stalling is by a second hydraulic controlsignal at least for rotation velocities within the second rotationalvelocity range. Control of displacement in the first rotational velocityrange of the variable displacement hydraulic pump is by a firsthydraulic control signal responsive to a high pressure hydraulic fluidoutput of the variable displacement pump. In the second rotationalvelocity range the second hydraulic control signal sets the position ofthe anti-stall piston with the first hydraulic control signal settingthe quantity of hydraulic fluid pumped to a hydraulic load.

A RAM air turbine in accordance with the present invention operates byaccelerating the blades from a stop through a third rotational velocityrange, through the second rotational velocity range into the firstrotational velocity range with the displacement of the variabledisplacement hydraulic pump being controlled in all three velocityranges. In the third rotational velocity range, the displacement of thepump is reduced to a displacement equal to or less than a displacementat which the variable displacement hydraulic pump operates within thesecond rotational velocity range which preferably is zero by destrokingthe displacement control of the variable displacement hydraulic pump tothe maximum extent under the control of an anti-stall piston controlledby a second hydraulic control signal. In the second rotational velocityrange, the displacement of the hydraulic pump may be increased inproportion to the rotational velocity of the blades within the secondrotational velocity range in response to the second hydraulic controlsignal to provide a variable stop. The first hydraulic control signalsets the quantity of pressurized fluid which is pumped. The displacementof the variable displacement hydraulic pump in the first rotationalvelocity range is controlled by a stroking piston controlled by a firsthydraulic control signal generated in response to a high pressurehydraulic fluid output of the variable displacement hydraulic pump. Theanti-stall piston does not reduce the displacement of the variabledisplacement hydraulic pump in the first rotational velocity range. Thesecond hydraulic control signal has a pressure which is directlyproportional to the rotational velocity of the blades and controls thedisplacement of the variable displacement hydraulic pump in the secondand third rotational velocity ranges.

A power controller, which provides reduced power emergency generatingcapability in the second rotational velocity range at which the priorart RAM air turbines were not capable of producing any output power whencompared to the emergency power generating capability in the firstrotational velocity range, has a hydraulic pressure relief whichfunctions to depressurize the coupling of the high pressure output fromthe variable displacement hydraulic pump from the displacement controlof the hydraulic pump to the anti-stall piston in the event of a failurein generating a pressurized hydraulic output from a pump, driven by theturbine blades, used for controlling the generation of the secondhydraulic control signal to control the anti-stall piston to control thedisplacement of the variable displacement hydraulic pump at least in thesecond rotational velocity range. The hydraulic pressure relief preventsthe anti-stall piston from overriding the stroking piston displacementcontrol of the variable displacement in the first rotational velocityrange in the event of the aforementioned failure of the pump inproducing the pressurized hydraulic output for controlling thegeneration of the second hydraulic control signal in controlling thedisplacement in the second rotational velocity range.

The variable displacement hydraulic pump includes a displacement controlhaving an anti-stall piston which is responsive to the second hydrauliccontrol signal for providing a variable stop varying the displacement ofthe variable displacement hydraulic pump for rotational velocities ofthe blades of the turbine in the second rotational velocity range and astroking piston which is responsive to a first hydraulic control signalfor varying displacement to the variable displacement hydraulic pump inthe first rotational velocity range which produces pressurized hydraulicfluid to drive a hydraulic load during rotational velocities in thefirst rotational velocity range.

A RAM air turbine for use in generating power for an aircraft by drivinga load from an airstream intercepting blades of the turbine as theaircraft moves through the air with the turbine applying power to theload during rotation of the blades in a first rotational velocity rangeand during rotation of the blades in a second rotational velocity rangewhich is lower than the first rotational velocity range in accordancewith the invention includes a variable displacement hydraulic pump whichis driven by rotation of the blades, including a displacement controlhaving an anti-stall piston which is responsive to a second hydrauliccontrol signal for varying the displacement of the variable displacementhydraulic pump for rotational velocities of the blades in the secondrotational velocity range and a stroking piston which is responsive to afirst hydraulic control signal for varying displacement of the variabledisplacement hydraulic pump in the first rotational velocity range, forproducing pressurized hydraulic fluid to drive a hydraulic load duringrotational velocities in the first and second rotational velocityranges; and wherein a reduced power output in the second rotationalvelocity range is produced when compared to power output which may beoutputted in the first rotational velocity range with the driven loadgenerating power for controlling the aircraft in the first and secondrotational velocity ranges. The pistons are coaxial and retained in acoaxial bore. The anti-stall piston has a diameter which is larger thana diameter of the stroking piston; and the bore has a first section anda second section with the diameter of the first section being largerthan a diameter of the second section with the second section stoppingmovement of the anti-stall piston. A hydraulic fluid source driven byrotation of the blades produces a pressurized hydraulic fluid outputwhich varies in pressure in proportion to the rotational velocity of theblades with the second hydraulic control signal being generated inresponse to the pressurized hydraulic fluid output; and the firsthydraulic control signal is generated in response to a high pressurehydraulic fluid output. The anti-stall piston is movable between firstand second positions in response to the second hydraulic control signalwhich causes the stroking piston to move between first and secondpositions with the first position of the stroking piston producing amaximum displacement of the variable displacement hydraulic pump and thesecond position of the stroking piston producing a minimum displacementof the variable displacement hydraulic pump; and the stroking piston ismovable between first and second positions independent of movement ofthe anti-stall piston in response to the first hydraulic control signalin the first rotational velocity range. The invention further includes apressure regulator hydraulically coupled to a high pressure output ofthe variable displacement pump which couples pressurized hydraulic fluidfrom the high pressure output to a lower pressure to regulate the outputpressure of the variable displacement hydraulic pump with the lowerpressure being the first hydraulic control signal. The anti-stall pistonis positioned in the first position during rotation of the blades in thefirst rotational velocity range.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates prior art RAM air turbines used for generatingemergency power on an airplane.

FIG. 2 illustrates a block diagram of an embodiment of the presentinvention.

FIG. 3 illustrates the variable displacement hydraulic pump used inaccordance with the present invention.

FIG. 4 illustrates the displacement control for the variabledisplacement hydraulic pump in accordance with the present invention.

FIG. 5 illustrates the constant power output characteristic of a RAM airturbine in accordance with the present invention which is operated inthe second rotational velocity range.

FIG. 6 illustrates the operation of the variable displacement hydraulicpump of the present invention for speeds in the third rotationalvelocity range.

FIG. 7 illustrates the operation of the variable displacement hydraulicpump of the present invention in the second rotational velocity range.

FIG. 8 illustrates the operation of the variable displacement hydraulicpump in accordance with the present invention for speeds in the firstrotational velocity range.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 illustrates a block diagram of an embodiment 30 of a RAM airturbine in accordance with the present invention. Like referencenumerals identify like parts in FIGS. 1 and 2. As illustrated, the RAMair turbine 30 is in the deployed position in which it has been pivotedfrom a stowed position in the fuselage identified schematically byreference numeral 33 to the deployed position as illustrated tointercept air on the blades 12 produced by motion of the airplane tocause rotation of the blades. It should be understood that the actualstowed and deployed positions are as illustrated in the assignee'scommonly assigned U.S. Pat. Nos. 4,717,095 and 4,742,976. The pivotingmechanism for moving RAM air turbines between the stowed and deployedpositions may be in accordance with the pivoting mechanism of U.S. Pat.Nos. 4,717,095 and 4,742,976 which are incorporated herein by referencein their entirety. The velocity of the airplane in moving through theair produces the RAM AIRSTREAM. The variable displacement hydraulic pump19 functions to produce pressurized hydraulic fluid 20 which is appliedto a hydraulic load 32. The hydraulic load 32 may be any hydraulic loadutilized in an airplane such as, but not limited to, a hydraulicactuator for moving of flight control surfaces or a hydraulic motorwhich is driven by the pressurized hydraulic fluid 20 to drive a load 36which may be an electrical generator for generating emergency electricalpower.

The operational characteristic of the RAM air turbine 30 differs fromthe prior art of FIG. 1 in that hydraulic power is generated for asecond rotational velocity range of the blades 12 below which thegovernor 16 cannot prevent stalling from occurring. While not limitedthereto, in a preferred embodiment of the present invention, the secondrotational velocity range is between 4600-5250 rpm in which the variabledisplacement hydraulic pump 19 produces a constant power output ofhydraulic fluid 20 varying in pressure in accordance with the powercharacteristics of FIG. 5 described below. The power which may beapplied from the rotation of the blades 12 to the hydraulic load 32 isless than the maximum power which may be applied to the hydraulic loadduring rotation of the blades in a first rotational velocity range.While not limited thereto, in the present invention the first rotationalvelocity range is above 5250 rpm. The first rotational velocity range iscontrolled by the operation of the governor 16 in varying the pitch ofthe blades 12 in association with the operation of a pressure regulatorcontained within the variable displacement hydraulic pump 19 asgenerally in the prior art. The invention's production of usefulhydraulic power from the variable displacement hydraulic motor 19 in thesecond rotational velocity range, from which no useful power wasproduced in the prior art, provides the pilot of an airplane in anemergency situation with a constant power output of a magnitude which isreduced in comparison to the power which may be drawn for rotation ofthe blades 12 within the first rotational velocity range. This powerprevents flying with no flight controls for velocities of the airplaneproducing rotational velocities of the blades in the second rotationalvelocity range with the resultant tremendous dangers.

The RAM air turbine 30 has a power controller 40, driven by rotation ofthe blades, for controlling power applied from the blades to the load asa function of airplane velocity in the second rotational velocity rangebelow the first rotational velocity range. It is important to note thatthe operation of the invention in the second rotational velocity rangeunder the control of the power controller 40 is independent of theoperation of the invention in the first rotational velocity range.Therefore, as explained in detail below with reference to FIG. 7,failure of the speed detector 46 of the power controller 40 does notdisable the generation of emergency power in the first rotationalvelocity range. The power controller 40 is comprised of a gearbox 42which supplies torque to the variable displacement hydraulic pump 19 bymeans of drive shaft 44, a speed detector 46, which is driven by torqueapplied from gearbox 42 through drive shaft 48 producing a controloutput 50 of pressurized hydraulic fluid applied to a displacementcontrol 52 controlling the displacement of the variable displacementhydraulic pump 19 in the second rotational velocity range. Pressurizedhydraulic fluid 54 applied to the displacement control 52 controls thedisplacement of the variable displacement hydraulic pump 18 in the firstrotational velocity range. The pressurized hydraulic fluid output 50from the speed detector 46 commands the displacement of the variabledisplacement hydraulic pump 19 to be reduced to zero for a thirdrotational velocity range of the blades 12 which extends from stop up tothe minimum velocity of the second rotational velocity range which inthe preferred embodiment of the present invention is 4600 rpm. Thehydraulic power provided by the pressurized hydraulic fluid 20 from thevariable displacement hydraulic pump 19 in the second rotationalvelocity range enables the pilot of an airplane to have power useful forcontrolling the flight control surfaces down to an airspeed ofapproximately 96 knots equivalent airspeed whereas the prior art RAM airturbine of FIG. 1 was subject to stall at approximately 125 knotsequivalent airspeed. The increased margin of safety provided to a pilotby providing reduced emergency power at velocities close to the stallvelocity of the aircraft substantially reduces the possibility cf a"dead stick" in the speed ranges between 100-125 knots to provide anincreased margin of safety to the pilot.

FIG. 3 illustrates a block diagram of the variable displacement pump 19,speed detector 46 and displacement control 52 of the RAM air turbine 30of the present invention. Like reference numerals identify like parts inFIGS. 2 and 3. The displacement control 52 is comprised of an anti-stallpiston 60 which is movable between a first position as illustrated inFIG. 3 and a second position located to the right with respect to FIG.3, a stroking piston 62, which is movable between a first position, asillustrated in FIG. 3, and a second position located to the right withrespect to FIG. 3 and a rate piston 64 which contacts a wobble plate(illustrated in FIG. 4) and applies force resisting the force applied byspring 66 to vary the displacement of the variable displacementhydraulic pump 19 which has a low pressure inlet 68 and a high pressureoutlet 70. The variable displacement hydraulic pump 19 is conventionaland is only illustrated schematically with respect to the low pressureinlet 68 and the high pressure outlet 70. The stroking piston 62 ismovable independently of the anti-stall piston 60 in the firstrotational velocity range. Movement of the anti-stall piston 60 duringthe second rotational velocity range under the control of a secondhydraulic control signal applied on a second hydraulic control circuit72 to the right with respect to FIG. 3 reduces the displacement of thevariable displacement hydraulic pump 19. The anti-stall piston 60provides a variable stop for the control of pressurized hydraulic fluidwhich may be delivered under the control of the stroking piston 62 whichcontrols the displacement of the variable displacement hydraulic pump 19under the control of the first hydraulic control signal on hydraulicline 148 as described below. Movement of the anti-stall piston 60 forcesthe stroking piston 62 outward from its recessed position within bore 74within the body 76. The bore 74 has a first section 78 and a secondsection 80 which are coaxial. The diameter of the first section 78 islarger than the diameter of the second section 80. The bottom 82 of thefirst section 78 stops movement of the anti-stall piston 60. Thestroking piston 62 moves independently of the anti-stall piston 60 andextends to the right from the position of FIG. 3 in reducing thedisplacement of the variable displacement hydraulic pump 19 from themaximum displacement as illustrated during rotational of the blades 12in the first and second rotational velocity ranges. In the firstrotational velocity range the anti-stall piston 60 is fixed in theposition as illustrated in FIG. 3. In the second rotational velocityrange, the anti-stall piston 60 varies from its first position with amaximum stop permitting maximum displacement to a minimum stop whichproduces minimum displacement (zero). The second hydraulic controlsignal, which controls the movement of the anti-stall piston 60 betweenthe first and second positions, is controlled by spool valve 90 whichcontains an axially movable spool 92 having lands 94-100. Lands 94 and96 are connected by section 102 having a reduced diameter which permitshydraulic fluid flow between the lands. Similarly, lands 96 and 98 areconnected by section 104 which permits hydraulic fluid flow between thelands. Finally, lands 98 and 100 are connected by section 106 whichpermits hydraulic fluid flow between the lands. The speed detector 46 isa gear pump which pressurizes hydraulic fluid from case pressure to ahigh pressure output which is connected to the bore 108 within the spoolvalve 90 by fluid coupling 110. A spring 112, which has an adjustablecompression adjusted by turning fitting 114, biases the spool to theleft. Rotation of the blades 12 causes rotation of the speed detector 46through the torque coupling 48 of FIG. 1 to pressurize hydraulic fluidat the output of the gear pump with a pressure which is directlyproportional to the rotational velocity of the blades 12. It should benoted that the gearbox 42 drives the variable displacement hydraulicpump 19 with a slightly different velocity than the rotational velocityof the input 14 with the difference being approximately 100 rpm at 5250rpm of the blades 12. The gear pump 46 produces a pressurized hydraulicfluid output which varies in pressure in proportion to the rotationalvelocity of the blades which produces a force acting on the spool 92 tothe right to cause movement of the spool to produce compression of thespring 112. The degree of movement controls the generation of the secondhydraulic control signal applied to the anti-stall piston by the secondhydraulic control circuit 72, the first hydraulic control signal appliedto the stroking piston 62 through the first hydraulic circuit 148 andthe commanding of the displacement of the variable displacementhydraulic pump 19 to the maximum displacement stop within the secondrotational velocity range when the gear pump 46 fails as discussedbelow. The orifice 114 develops a pressure differential across therespective ends of the spool 92 which is equal to the difference betweenthe high pressure output from the gear pump 46 and the inlet pressure atthe inlet 68 of the variable displacement hydraulic pump 19. Thepressure differential across orifice 114 produces a high speed responsein the spool 92 in moving in response to increased rotational velocityof the blades 12 which provides high speed pressure changes in responseto changing hydraulic load conditions. The function of the lands 94-100is described in detail below. The second hydraulic circuit 72 contains abifurcation 120 with a first part 122 connected to a first axialposition 124 of the bore 108 of the spool valve 90 in which the spool 92moves and a second part 126 connected to a second axial position 128separated from the first axial position by an axial displacement. Thesecond section 126 functions to bleed high pressure hydraulic fluidtrapped in the second hydraulic circuit 72 which is produced by the highpressure output 70 being coupled to the second hydraulic circuit withinthe second rotational velocity range when the gear pump 46 fails. Inthis situation, the trapped high pressure hydraulic fluid within thesecond hydraulic circuit 72 bleeds from the first hydraulic circuit tothe case pressure across the axial displacement by bypassing the land 98to a hydraulic circuit 130 which is connected to the inlet 68 of thevariable displacement hydraulic pump 19. As a result, the system willoperate in accordance with the prior art which permits emergency powerto be generated in the first rotational velocity range.

The movement of the spool 92 in response to the pressurized hydraulicfluid output from the gear pump 46 to the right in generating the secondhydraulic control signal applied to the anti-stall piston 60 in thethird rotational velocity range is described as follows. For speeds fromzero to 4600 rpm, the spool 92 moves a distance axially within the bore108 of the spool valve 90 which is proportional to the pressure of thepressurized hydraulic fluid output from the gear pump 40. Movement ofthe spool 92 to the right, in response to the pressurized hydraulicfluid output from the gear pump 46, within the bore 108 of the spoolvalve 90 connects high pressure hydraulic fluid circuit 140, which isconnected to the high pressure outlet of the variable displacementhydraulic pump 19, to the second hydraulic fluid circuit 72 when theedge 142 of the land 98 moves to the right sufficiently to be at leastaxially aligned with the axial position 144 at which the high pressurehydraulic circuit 140 is connected to the bore 108 of the spool valve90. At this position and positions to the right, the spool 92 permitsfluid flow in the reduced diameter section 104 between the high pressureoutput 70 through hydraulic circuit 140 to the first hydraulic circuit72 to cause the anti-stall piston 60 to move from the first position tothe second position commanding zero displacement for the variabledisplacement hydraulic motor 19. The spool 92 moves proportionally tothe right as the rotational velocity of the blades 12 increases.

When the rotational velocity of the blades 12 reaches the lowest speedin the second rotational velocity range, the right hand part of the land96 is located just to the left of the axial position 124 in a firstposition. As the rotational velocity of the blades 12 within the secondrotational velocity range increases, the land 96 moves from the firstposition to the right toward a second position to begin to occlude theinlet port 146 of the second hydraulic circuit 72 to proportionallyreduce the pressure of the hydraulic coupling between the high pressureoutlet 70 of the variable displacement hydraulic pump 19 and theanti-stall piston 60. The anti-stall piston 60 is positioned in a secondstop position causing the stroking piston 62 to be positioned at thesecond position to command a zero flow rate from the variabledisplacement hydraulic motor 19 as the land 96 begins to occlude theinlet port 146. The pistons 60 and 62 proportionally move from a secondposition commanding the minimum displacement (zero) to their firstposition which commands the maximum displacement stop of the variabledisplacement hydraulic pump in proportion to the degree of occlusion ofthe inlet port 146 by the land 96. At the lower limit of the firstrotational velocity range, the pistons 60 and 62 are positioned in theirfirst position to command a maximum displacement stop of the variabledisplacement hydraulic pump 19 and the land 96 is located in its secondposition.

For rotational velocities within the first rotational velocity range ofthe blades 12, the anti-stall piston 60 is withdrawn to its firstposition with a maximum displacement stop. A first hydraulic controlsignal applied on the first hydraulic circuit 148 to the stroking piston62 controls the displacement of the variable displacement hydraulicmotor 19 in proportion to the difference in pressure between the highpressure output 70 of the variable displacement hydraulic pump and alower pressure present in the first hydraulic circuit produced by thepressure regulator 150. The pressure regulator 150 contains a springbias 152 having an adjustable compression which is adjusted by turningof threaded member 154. The high pressure hydraulic fluid output formthe high pressure output 70 of the variable displacement hydraulic motor19 is bled to a lower pressure which is the first hydraulic controlsignal within the first hydraulic circuit 148 under the action of thepressure regulator 150. The movable member 156 moves axially within thebore 158 of the pressure regulator 150 to bleed a portion of the highpressure hydraulic fluid from the high pressure output 70 to a lowerpressure to produce a first hydraulic control signal which is thepressure for controlling the displacement of the stroking piston to varythe displacement of the variable displacement hydraulic motor 19. Thedisplacement of the variable displacement hydraulic pump 19 in the firstoperational range is controlled by the pressure drop between the highpressure output 70 of the variable displacement hydraulic pump and thepressure of the second hydraulic control signal which varies under theaction of the bias applied by spring 152 in regulating the outputpressure. The pressure regulator 150 controls the pressure in the output70 of the variable displacement hydraulic motor within a narrow rangesuch as, but not limited to, 3,000-3,200 psi.

FIG. 4 illustrates the displacement control mechanism for the variabledisplacement hydraulic pump 19 utilized with the present invention. Likereference numerals identify like parts in FIGS. 2-4. FIG. 4 illustratesthe displacement of the variable displacement hydraulic pump 19 reducedto zero during rotation of the blades 12 in the first rotationalvelocity range. The stroking piston 62 rides on a slipper 200 attachedto one end of a wobbler 202. The rate piston 64 rides on a slipper 200attached to an opposed end of the wobbler which applies force throughthe action of compression of spring 66 against the extension of thestroking piston 62 caused by the first hydraulic control signal. Thewobbler 202 pivots about axis 204 in a conventional manner. Thedisplacement of the variable displacement hydraulic pump is proportionalto the angle of inclination of the wobbler 202 with respect to the axisof rotation 204. The maximum displacement of the variable displacementhydraulic pump 19 occurs when the anti-stall piston 60 is fullywithdrawn into the body 52 torching the bottom end of the strokingpiston 62. Pistons 206 sweep out bores within the barrel cylinder 208 topressurize hydraulic fluid from a low pressure inlet 68 to a highpressure outlet 70 which is carried in a port plate (not illustrated) ina conventional manner. During operation in the second rotationalvelocity range, the anti-stall piston 60 moves from the position asillustrated to an extended position which forces the stroking piston 62outward to vary the displacement of the variable displacement hydraulicpump 19 from a maximum displacement stop to a minimum displacement stopas illustrated in FIG. 4 with it being understood that the anti-stallpiston is in contact with the stroking piston in this mode of operation.The variation in the maximum displacement stop in the second rotationalvelocity range is proportional to the rotational velocity of the blades12.

FIG. 5 illustrates the operational characteristic of the variabledisplacement hydraulic motor 19 within the second rotational velocityrange. The ordinate is in units of liters per minute of hydraulic fluidand the abscissa is in terms of pressure units of bars with each barbeing equal to one atmospheric pressure. The constant power curvesproduced by the operation of the controller 40 of FIG. 5 are from speedsof 4650-5350 rpm of the variable displacement hydraulic pump 19. Itshould be understood that the pump is driven by the gearbox 42 with agear ratio slightly greater than 1 with the blade speed at 5350 rpm ofthe variable displacement hydraulic pump 19 being 5250 rpm in apreferred embodiment of the present invention. The pressure regulator150 functions in conjunction with the operation of the anti-stall andstroking pistons 60 and 62 to provide pressurized hydraulic fluid at thehigh pressure output 70 of the variable displacement hydraulic pump 19having constant power for each velocity within the second rotationalvelocity range. For each velocity within the second rotational velocityrange, the power controller 40 produces a constant power curve 300. FIG.5 only illustrates two constant power curves 300 of a whole family ofcurves with it being understood that each distinct velocity within thesecond rotational velocity range has its own unique constant power curve300.

The control characteristic 300 produced by the power controller 40within the second rotational velocity range represents a reduced poweroutput, when compared to the maximum power which could be produced bythe variable displacement hydraulic pump 19 within the first rotationalvelocity range, which was not available in the prior art. The constantpower curves 300 in the second rotational velocity range of the blades12 represent the output of useful power for controlling flight surfacesand/or generating electric power in velocity ranges at which a stallcondition would have occurred in the prior art. Each constant powercurve 300 has a decreasing flow rate as the pressure of the hydraulicfluid increases which is applied to the hydraulic load 32.

FIG. 6 illustrates the operation of the variable displacement hydraulicpump 19 at zero rpm for blade velocities within the third rotationalvelocity range which in a preferred embodiment of the present inventionis from zero to 4600 rpm at which the blades 12 are not coupled to thevariable displacement hydraulic pump 19 for producing emergency power soas to permit the blades to attain a velocity within the secondrotational velocity range. The variable displacement hydraulic pump 19operates in the off loaded rotational velocity range without thevolumetric fuse of the prior art. The present invention uses the powercontroller 40 to control the generation of emergency power in the secondrotational speed range and performs the function of the prior artvolumetric fuse with the power controller for operation in the thirdrotational velocity range thereby eliminating the problems of thevolumetric fuse as discussed above. Like reference numerals identifylike parts in FIGS. 3 and 6. Hydraulic pressure at various points withinFIG. 6 is encoded with the key in the bottom right-hand corner. As therotational velocity of the blades 12 increases the output pressure fromthe gear pump 46 on output 110 increases proportionately. The increasedpressure forces the spool 92 to the right. When the edge 142 of land 98moves past axial position 144, high pressure hydraulic fluid is coupledfrom the output 70 through reduced diameter section 104 between lands 96and 98 to the second hydraulic line 72 to cause the anti-stall piston 60and the stroking piston 62 to move all the way to the right to cause thedisplacement of the variable displacement hydraulic pump 19 to be set tozero. With respect to FIG. 4 the anti-stall piston 62 would movedownward into contact with the stroking piston 62 to cause the wobblerplate 202 to assume the position as illustrated. As the rotationalvelocity of the blades 12 increases, the spool 92 moves proportionatelyto the right. At 4600 rpm, the land 96 begins to occlude the inlet tothe second hydraulic control line 72 which causes the anti-stall piston60 and the stroking piston 62 to move from a fully extended position(not illustrated) wherein the displacement of the variable displacementhydraulic pump 19 is at a minimum (zero) toward the position, asillustrated in FIG. 6, which represents the position of the first andsecond hydraulic control pistons below 300 rpm.

FIG. 7 illustrates the operation of the variable displacement hydraulicpump 19 at 4600 rpm for blade velocities within the second rotationalvelocity range which in a preferred application of the present inventionis between 4600-5250 rpm. This is the range of rotational velocities inwhich useful power is outputted from the variable displacement hydraulicmotor 19 under the control of the power controller 40 at a rate which isless than the power which may be outputted by the variable displacementhydraulic pump in the first rotational velocity range and which is powerwhich was not available in the prior art as a consequence of stalling ofthe blades 12 because of the inability of the governor 16 to reduce thecoupling of power produced by the blades to the hydraulic load 32. Likereference numerals identify like parts in FIGS. 3, 6 and 7. Movement ofthe anti-stall piston 60 and the stroking piston 62 is bidirectional inthe second rotational velocity range. As illustrated with the velocityof the blades being at the minimum velocity in the second rotationalvelocity range the movement of the anti-stall piston 60 and the strokingpiston 62 is to the left as indicated by the single direction arrowspointing to the left for both pistons. The output power is in accordancewith the constant power curves of FIG. 5 discussed above. As therotational velocity of the blades 12 increases from 4600 rpm, the land96 begins to occlude the inlet port 146 to cause a drop in pressure inthe second hydraulic control line 72 which causes the displacement stopof the variable displacement hydraulic pump 19 to be increased from zeroat 4600 rpm until it reaches its maximum displacement stop at 5250 rpm.The pressure regulator 150 functions in conjunction with the variationin the displacement stop of the variable displacement hydraulic pump tocause the constant power characteristic of the curves 300 as describedabove with respect to FIG. 5 to be produced for the speed at which theairplane is flying with the hydraulic demand represented by thehydraulic load 32 causing the flow rate and pressure to vary inaccordance with the constant power curves. At 5250 rpm, the control ofthe displacement of the variable displacement hydraulic pump is nolonger under the control of the second hydraulic control line 72 as aconsequence of the inlet pressure being coupled to the second hydrauliccontrol line through the reduced diameter section 102 of the spool 92.

FIG. 8 illustrates the operation of the variable displacement hydraulicpump 19 in the first rotational velocity range which in a preferredapplication of the present invention is above 5250 rpm with the strokingpiston 62 being positioned at maximum displacement. In the firstrotational velocity range, the governor 16 in combination with thepressure regulator 150 controls the operation of the system such thatthe pitch of the blades 12 and the pressure of the hydraulic fluidoutputted on the high pressure output 70 is within a specified pressurerange, such as between 3,000-3,200 psi. In this operational range ofvelocities of the blades 12 the stroking piston 62 moves independentlyoutward from the anti-stall piston as illustrated in FIG. 4 wherein theanti-stall piston is fully withdrawn into the bore 78 as illustrated inFIG. 8. The anti-stall piston 60 does not move from the first positionas illustrated during operation within the third speed range. Theposition of the anti-stall piston 62 varies from the first position asillustrated in FIG. 8 wherein a maximum displacement of the variabledisplacement hydraulic pump 19 is produced to a second position in whichthe stroking piston 62 is fully extended as illustrated in FIG. 4wherein zero displacement of the variable displacement hydraulic pump isproduced. The movement of the stroking piston 62 is illustrated by thesingle one direction arrow pointing to the left from the strokingpiston. The demands placed on the variable displacement hydraulic pump19 by the hydraulic load 32 cause the stroking piston 62 to vary inbetween the first and second positions. The variation between the firstand second positions is a function of the pressure drop from the outputof the high pressure cutlet 70 to case pressure which is the hydrauliccontrol signal for the stroking piston 62. The displacement of thevariable displacement hydraulic pump 19 in the first rotational velocityrange is inversely proportional to the pressure drop between the highpressure output 70 and case pressure which is produced by the operationof the spool 158 within the pressure regulator 150. Movement of thespool 158 in response to the change in output pressure on the outlet 70causes the pressure drop between the high pressure output and casepressure to vary which modulates the position of the stroking piston 62in a manner inversely proportional to the pressure. The anti-stallpiston 60 does not move from the position as illustrated in FIG. 8during operation within the first rotational velocity range as aconsequence of the governor 16 and the pressure regulator 150controlling the coupling of power from the variable displacementhydraulic motor 19 to the hydraulic load 32.

The larger diameter of the anti-stall piston 60 in comparison to thediameter of stroking piston provides for the anti-stall piston to have aquick response to small pressure differences between the first andsecond hydraulic control signals. As a result, the displacement of thevariable displacement hydraulic pump is rapidly varied to preventstalling and production of constant power in accordance with theconstant power characteristics 300 of FIG. 5.

While the invention has been described in terms of its preferredembodiments, it should be understood that numerous modifications may bemade thereto without departing from the spirit and scope of theinvention as defined in the appended claims. It is intended that allsuch modifications fall within the scope of the appended claims.

We claim:
 1. A ram air turbine for use in generating power for an aircraft by driving a load with an airstream intercepting blades of the turbine as the aircraft moves through the air with the turbine applying power to the load during rotation of the blades in a first rotational velocity range and during rotation of the blades in a second rotational velocity range which is lower than the first rotational velocity comprising:a variable displacement hydraulic pump which is driven by rotation of the blades, including a displacement control having an anti-stall piston which is responsive to a second hydraulic control signal for varying the displacement of the variable displacement hydraulic pump for rotational velocities of the blades in the second rotational velocity range and a stroking piston which is responsive to a first hydraulic control signal for varying displacement of the variable displacement hydraulic pump in the first rotational velocity range, for producing pressurized hydraulic fluid to drive a hydraulic load during rotational velocities in the first and second rotational velocity ranges; and wherein a reduced power output in the second rotational velocity range is produced when compared to power output which may be outputted in the first rotational velocity range with the driven load generating power for controlling the aircraft in the first and second rotational velocity ranges.
 2. A ram air turbine in accordance with claim 1 wherein:the pistons are coaxial.
 3. A ram air turbine in accordance with claim 2 wherein:the pistons are retained in a coaxial bore.
 4. A ram turbine in accordance with claim 3 wherein:the anti-stall piston has a diameter which is larger than a diameter of the stroking piston; and the bore has a first section and a second section with a diameter of the first section being larger than a diameter of the second section with the second section stopping movement of the anti-stall piston.
 5. A ram air turbine in accordance with claim 1 wherein:a hydraulic fluid source driven by rotation of the blades produces a pressurized hydraulic fluid output which varies in pressure in proportion to the rotational velocity of the blades with the second hydraulic control signal being generated in response to the pressurized hydraulic fluid output; and the first hydraulic control signal is generated in response to a high pressure hydraulic fluid output.
 6. A ram air turbine in accordance with claim 2 wherein:a hydraulic fluid source driven by rotation of the blades produces a pressurized hydraulic fluid output which varies in pressure in proportion to the rotational velocity of the blades with the second hydraulic control signal being generated in response to the pressurized hydraulic fluid output; and the first hydraulic control signal is generated in response to a high pressure hydraulic fluid output.
 7. A ram air turbine in accordance with claim 3 wherein:a hydraulic fluid source driven by rotation of the blades produces a pressurized hydraulic fluid output which varies in pressure in proportion to the rotational velocity of the blades with the second hydraulic control signal being generated in response to the pressurized hydraulic fluid output; and the first hydraulic control signal is generated in response to a high pressure hydraulic fluid output.
 8. A ram air turbine in accordance with claim 4 wherein:a hydraulic fluid source driven by rotation of the blades produces a pressurized hydraulic fluid output which varies in pressure in proportion to the rotational velocity of the blades with the second hydraulic control signal being generated in response to the pressurized hydraulic fluid output; and the first hydraulic control signal is generated in response to a high pressure hydraulic fluid output.
 9. A ram air turbine in accordance with claim 5 wherein:the anti-stall piston is movable between first and second positions in response to the second hydraulic control signal which causes the stroking piston to move between first and second positions with the first position of the stroking piston producing a maximum displacement of the variable displacement hydraulic pump and the second position of the stroking piston producing a minimum displacement: of the variable displacement hydraulic pump; and the stroking piston is movable between first and second positions independent of movement of the anti-stall piston in response to the first hydraulic control signal in the first rotational velocity range.
 10. A ram air turbine in accordance with claim 9 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which shunts pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal.
 11. A ram air turbine in accordance with claim 6 wherein:the anti-stall piston is movable between first and second positions in response to the second hydraulic control signal which causes the stroking piston to move between first and second positions with the first position of the stroking piston producing a maximum displacement of the variable displacement hydraulic pump and the second position of the stroking piston producing a minimum displacement of the variable displacement hydraulic pump; and the stroking piston is movable between first and second positions independent of movement of the anti-stall piston in response to the first hydraulic control signal in the first rotational velocity range.
 12. A ram air turbine in accordance with claim 11 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which shunts pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal.
 13. A ram air turbine in accordance with claim 7 wherein:the anti-stall piston is movable between first and second positions in response to the second hydraulic control signal which causes the stroking piston to move between first and second positions with the first position of the stroking piston producing a maximum displacement of the variable displacement hydraulic pump and the second position of the stroking piston producing a minimum displacement of the variable displacement hydraulic pump; and the stroking piston is movable between first and second positions independent of movement of the anti-stall piston in response to the first hydraulic control signal in the first rotational velocity range.
 14. A ram air turbine in accordance with claim 13 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which shunts pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal.
 15. A ram air turbine in accordance with claim 8 wherein:the anti-stall piston is movable between first and second positions in response to the second hydraulic control signal which causes the stroking piston to move between first and second positions with the first position of the stroking piston producing a maximum displacement of the variable displacement hydraulic pump and the second position of the stroking piston producing a minimum displacement of the variable displacement hydraulic pump; and the stroking piston is movable between first and second positions independent of movement of the anti-stall piston in response to the first hydraulic control signal in the first rotational velocity range.
 16. A ram air turbine in accordance with claim 15 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which couples pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal.
 17. A ram air turbine in accordance with claim 10 wherein:the first piston is positioned in the first position during rotation of the blades in the first rotational velocity range.
 18. A ram air turbine in accordance with claim 12 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which couples pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal.
 19. A ram air turbine in accordance with claim 14 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which couples pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal.
 20. A ram air turbine in accordance with claim 16 further comprising:a pressure regulator hydraulically coupled to a high pressure output of the variable displacement pump which couples pressurized hydraulic fluid from the high pressure output to a lower pressure to regulate the output pressure of the variable displacement hydraulic pump with the lower pressure being the second hydraulic control signal. 